MATEC Web of Conferences 22, 030 2 5 ( 2015)
DOI: 10.1051/ m atec conf/ 2015 2 2030 2 5
C Owned by the authors, published by EDP Sciences, 2015
Literature Review of Research on the Technology of Wire Rope Nondestructive Inspection in China and Abroad
Jie Tian, Junying Zhou*, Hongyao Wang & Guoying Meng
School of Mechanical Electronic and Information Engineering, China University of Mining and Technology,
Beijing, China
ABSTRACT: As consumables in mine, wire ropes have great significance for safe operation of coal mines. The
complex structure makes the nondestructive testing particularly difficult. This paper summarizes the existing
methods of analysis at home and abroad from the perspective of strong magnetic and weakly magnetic; introduces the main methods of wire rope at the present, including principle and current status. At last, several critical
problems in nondestructive testing of wire rope are discussed.
Keywords:
wire rope; nondestructive testing technology; electromagnetic detection method
1 INTRODUCTION
As one of the most important flexible members, wire
rope has high tensile strength and fatigue resistance,
light weight, good elasticity, stable and reliable under
dynamic load and overload ability and many other
advantages. It is widely used in mine, metallurgy,
ports, construction and other major industries of national economy and the improvement of department,
transport and traction equipment. Wire ropes are
widely used in in some areas such as cranes, oil drilling rig, elevators, and mine hoist. As a bearing component, wire rope will appear fatigue, corrosion, and
even a sudden break because of various reasons. Its
bearing capacity and reliability have the direct bearing
on the safety of equipment and people. Because of the
complicated structure of wire rope, the diversity of the
work environment, the limitations of detection methods and the development of manufacturing technique,
which make the defect detection of wire rope difficulty. It is very important to develop the nondestructive
testing equipment which can detect the status of wire
rope reliably. The nondestructive inspection technology of wire rope will be gradually developed.
There should be an appropriate detection method to
conduct the nondestructive testing of wire rope. At
present, there are many methods for nondestructive
testing of wire rope including electromagnetic detection, ultrasonic detection method, X-ray detection,
acoustic emission detection method, eddy current
testing method and so on. The electromagnetic detection method has been widely used and promoted. The
nondestructive detection method of wire rope will be
analyzed and the status of the various detection methods will be introduced in the following parts.
2 ANALYSIS OF THE PRESENT NONDESTRUCTIVE DETECTION METHOD OF WIRE
ROPE
According to the nature and characteristics of the
damage of wire rope, the damage of wire rope can be
divided into Localized Flaw and Loss of Metallic Area
[1]. The damage of LF refers to the wire rope damage
which is locally produced, including the broken of
internal and external, corrosion and local deformation.
The characteristics of LF are that metallic
cross-sectional area of wire rope which is suddenly
decreased. The damage of LMA refers to the effective
metallic sectional area of wire rope decrease slowly in
an axial longer range, including wear, long distance of
corrosion, and attenuation of wire diameter. The characteristics of LMA are that the metallic sectional area
of wire rope which is slowly decreased in a longer
range. Corresponding to these two kinds of damage,
the traditional detection methods can be divided into
LF magnetic flux leakage method [2], LMA/LF main
flux method and LMA/LF loop flux method. The
acoustic emission ultrasonic detection method which
is lately claimed has been widely used.
2.1 Inspection technology based on strong magnetism
The wire rope with good permeability was evenly
magnetized along the axial direction. If the magnetization section of wire rope has a loss, it can appear in the
magnetic leakage which causes the change of magnetic flux in magnetic circuit. Through the measurement
of magnetic flux surface leakage of wire rope, it can
detect the local damage such as broken wire and pitting. Through the measurement of main magnetic flux
in magnetic circuit of wire rope, the damage of
cross-sectional area and broken wire can be qualitatively detected. According to the different of detecting
*Corresponding author: zhoujunying716@163.com
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits
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MATEC Web of Conferences
element, strong magnetic detection can be divided into
the following kinds.
2.1.1 Detection method based on Hall Sensor
The Hall sensor detective method is a way which uses
the Hall sensor as a sensor to detect flux changes of
wire rope. Hall sensor is the semiconductor to which
Hall effects are applied. The structure between the
Hall sensor and the coil sensor are similar. But the
former detective device is the Hall sensor which is set
on the inner wall of the sensor. The latter is the induction coil which is around the wire rope. The detection
principle of Hall sensor is that it placed near the surface of leakage magnetic field on the surface of wire
rope and output the corresponding voltage signal.
Although eliminating the impact which velocity has
on signal amplitude, it still needs to transfer the signal
of time domain to the spatial domain. The signal on
the timeline will be stretched or compressed along
with sampling speed, because the detective speed is
not constant.
Hall sensor detective method being researched and
applied abroad includes: From 1960s to 1990s, Kitzinger F. and Wint G.A. put forward an idea of using
the Hall sensor as detecting device. The method tests
the cross-sectional and partial area of wire rope and
confirm the damage if it exists. Zawada Company has
a Hall sensor which can accurately detect all serious
defects including its position and depth. Local damage
detection accuracy is 0.2% for the cross-sectional area
of the wire rope [3]. Germany University of Stuttgart
have designed a kind of sensor probe which is set the
lining circular array with Hall sensors. It can clearly
describe the wire rope of the axial and circumferential
magnetic field [4].
Hall sensor detective method being researched and
applied in the domestic includes: Yang Shuzi, Kang
Yihua and other professors that come from Huazhong
University of Science and Technology began to study
the broken wire rope detection technology since 1980s.
They used rare earth permanent magnet as excitation
device which could activate wire rope. This method
measured leakage magnetic field around the wire rope
with the integrated Hall sensors. Through MTC-94
type of wire rope flaw detector and GDJY series of
quantitative broken detector of wire rope, it achieves
the quantitative detection of broken wire rope [5]. Tao
Dexin of Wuhan University of Science and Technology uses the testing method of magnetic flux leakage
by four Hall sensors to get the magnetic flux leakage
signals and detect the wire rope damage qualitatively.
Tan Jiwen et al in Qingdao University of Science and
Technology design the steel wire rope exciter according to the principle of magnetic bridge circuit. They
test the cross-sectional area of wire rope damage by
Hall sensors [6]. Hunan Institute of Science and
Technology applied for invention of detection device
for broken wires, Hall sensors detect larger magnetic
flux leakage after detection making alarm circuit light
and buzzer [7].
2.1.2 Detection method based on fluxgate sensor
Fluxgate detection is to obtain the testing signal by
detecting the magnetic leakage field of wire rope defection. First of all, make the fracture defect produces
the leakage magnetic field by using AC magnetic field
for excitation. After that, the voltage in the coil will
produce the symmetry changes, which can obtain the
testing signal.
As shown in Figure 1, establish a loop by setting up
single core and single coil sensor uniformly around
the wire rope. Sensor signals perform badly by reverse
tandem. Use AC magnetic field for excitation to remove the fixed wave signal brought by the wire rope.
Therefore, it can increase the signal to noise ratio and
restrain the mold interference in the detection of wire
rope effectively. The advantages of fluxgate detection
method are the high sensitivity and direction. The
disadvantages are the complicated calculation, the
enormous AC excitation equipment and difficult installation.
Figure 1. Fluxgate Assay
Canada Rotesco’s Rotescograph 2D and
2C-TAG88M use fluxgate sensor [8]. It has higher
detection accuracy to the local damage and the cross
sectional area of the damage. The minimum length of
the cross-sectional area damage can be resolved for
250~530mm. Gu Weixin from Shanghai Maritime
University detects wire ropes by magnetic flux gate.
Magnetic flux leakage signals of the defects on the
surface of wire rope will be collected by the
non-destructive detection probe based on single core
and winding flux gate [9]. It has established the
mathematical model [10] of wire rope testing signal
and deduced the correlation function between the
measured magnetic fields and the output voltage while
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adopting fluxgate detection of leakage magnetic field.
2.1.3 Detection method based on induction coil
The induction coil detection method is using permanent magnet to make the wire rope measured in deep
saturation along the axial direction of the wire rope.
Measure the damage of sectional area by measuring
the axial flux of wire rope. Distinguish the local damage of wire rope by measuring the magnetic flux
leakage of the surface of wire rope. The coil of induction coil detection method is gradually developed into
a differential coil, and then split it into a differential
coil. The biggest advantage of inductive coils is the
low cost and easy to implement. The big drawback is
that the speed of the rope detection greatly restricts the
output signal of the sensor. Maintain high detection
precision which is necessary to maintain the quantitative detection coil sensor speed. Instability detection
speed will make the sensor signal changed. As shown
from the pictures, Figure 2 is the original structure.
Figure 3 is differential and Figure 4 is split differential
coil. It emerged the first wire rope flaw which uses the
AC induction coil sensor excitation in 1906. At present, the way of induction is developed from the AC
excitation and DC excitation induction method into
permanent DC excitation which is extensively used [2].
Dr. H.R. Weischedel from American NDT conducted
in-depth research. He made improvements to the detection coil and the coil detector circuit is added to the
integrator circuit [11]. This detection device can quantitatively detect the damage of LMA, while the LF
damage can be qualitatively analyzed. In China, Harbin Institute of Technology and a branch of Fushun
Coal Mine using SCM system was successfully developed a GST-type wire rope flaw [12] which could
detect LMA and LF simultaneously.
Figure 4. Split Differential Coil
2.2 Inspection technology based on weak magnetic
field
The founding principle of weak magnetism inspection
technology is the ‘Spatial Magnetic Field Vector Resultants’ theory. As an innovative and proven NDT, it
adopts large air-space and non-contact weak magnetic
testing devices. It is capable to detect quantitatively
both internal and external flaws of the test wire rope
by monitoring and extracting signals of magnetomotive force changes of the testing wire rope, which is
preconditioned by weak magnetic loader. According
to quantum mechanics, ‘magnetic domains’ exist
among adjacent electrons of ferromagnetic medium,
which are lined up in a certain shape because of the
interactive and coupling effect of the electrons spin
magnetic moment. In each magnetic domain, the direction of spin magnetic moment is same. W sensors
are based on ‘spatial magnetic field vector resultants’
theory. The energy releasing device provides a given
weak electromagnetic field Bx, which interacts with
the weak magnetic field B in each cross section of the
test wire rope. They all generate the inductive magnetic field By, while the magnetism evaluating device
converts the magnetometive force changes of By into
electric signals (See Figure 5).
Luoyang TCK Wire Rope Testing Technology Co.,
Ltd uses a new method to detect a variety of injuries
quantitatively. Its TCK-BX can accurately evaluate
the residual bearing capacity, the safety coefficient
and the in-service life of wire rope.
2.3 Acoustic emission-ultrasonic testing method [2]
Figure 2. Original structure
Figure 3. Differential coil
For the quantitative detection of the rope injury situation, in recent years, scholars at abroad also proposed
a novel detection method that is acoustic emission ultrasonic testing method, which developed on the
basis of the respective advantages of comprehensive
ultrasonic acoustic emission (such as Figure 6). A set
of transducers and evil mixture is introduced to the
rope ultrasonic detection, modeling of acoustic emission signal characteristics of propagation in the rope;
another set of transducers and evil mixture extract the
signal, which is after amplification and sends the entry
limit controller. And then calculate the stress wave
coefficient to achieve quantitative identification rope
defects. The testing method of acoustic emission -
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Figure 5. A Cross-sectional element
Figure 6. Acoustic emission-ultrasonic schematic
ultrasonic can not only carry out the rope defect detection and defect characterization, but also assess the
fatigue damage of wire rope and internal performance
including strength and hardness. This makes up the
insignificancy of acoustic emission detection that only
detecting stationary wire rope and capturing instantaneous signal of broken rope. Nevertheless, the method
is still in the theoretical stage.
2.4 X-ray detection method [13]
When using ray to defect, different defects will have
different fading. As shown in Figure 7, the ray intensity is J0 and the ray intensity which passes through the
workpiece and defects are Jδ and JX. According to
different ray intensity that film accepted, black poor
parts are obviously reflected after washing. It can
identify the defects of shape, position and so on.
Some domestic enterprises have a certain amount of
research on X-ray detection. The x-ray detection device invented by Shanxi Hui Da uses different x-ray
absorption rate having different density of material to
make steel belt speed, high precision, full-face real-time scanned.
Figure 7. X-ray detection principle
3 PROBLEMS OF NONDESTRUCTIVE TESTING
OF WIRE ROPE TO BE SOLVED IN THE FUTURE
(1) Monitor the magnetic signal of fatigue damage of
wire rope [14]. Using the magnetic detection technology to monitor the fatigue damage of ferromagnetic
material is a new research direction on non-destructive
testing techniques in recent years. Microstructure of
ferromagnetic material is changed and it makes char-
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acteristics of magnetization changed, which causing
fatigue damage. If the magnetic flux leakage detection
technology is used to monitor the rope, the electromagnetic detection technology of wire rope will be
lifted to a new level.
(2) The wire rope detection is easily disturbed. Using Hall element as a sensor, it will under electromagnetic interference. If it is near strong electromagnetic wave, the waveform will be detected interference.
This appears larger fluctuation, which will affect the
results of analysis. How to reduce or eliminate interference remains to be further studied.
(3) The relationship between the signal of LF and
LMA and the strength loss of rope are uncertain. The
purpose of detecting wire rope is to assess the damage
of it. If we can build a mathematical model between
LMA and residual strength with rope, then we will
easily grasp the strength loss of rope. With the development of science and technology, it will become
inevitable to develop intelligent equipment that can
detect LMA and LF simultaneously.
(4) Reliability and usefulness of detection methods.
Although there are some practical testing equipment at
home and abroad, it can influence the results because
of restrictions on principles and applications. So the
reliability and correlation can’t be satisfied to the application requirements of actual production site. Only
as a secondary detection tool, its price and ease of use
can be restricted.
4 CONCLUSION
So far, the main problems existing in technology and
equipment of nondestructive testing of wire rope are
low reliability, low intelligence, the lack of objectivity
about test results and the incomplete information
about the damage of wire rope. Thus we can’t make
fully estimations for the damage of wire rope. So we
need to carry out exploratory research on the basis of
the existing flaw detector and develop a new technology with high performance and reliability to meet the
need of on-line detection. Through the deep analysis
of various factors, we can quantify the scale of the
influence of various factors on the grading and make
grading standard for reference and contrast.
ACKNOWLEDGMENTS
The authors would like to thank the National Natural
Science Foundation of China (No.51404276) and The
Central Business Funds of Colleges (No.2014QJ01)
for providing the financial support for conducting this
research. The authors also thank the reviews for their
useful comments and suggestions for improving the
present manuscript.
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